Park Highlights

Obed

National Wild and Scenic River

Tennessee

Obed Wild and Scenic River, Tennessee

Soils

Soils of the Cumberland Plateau are
primarily derived from sandstone, shale,
and siltstone. These are predominantly
loamy soils with moderate infiltration rates.
Soil depths of less than I to 5 feet (0.3 to
1.5 meters) occur over most of the plateau
such that overburden soil rarely serves as
a source of groundwater in upland areas.
Along the steep slopes of the mountains
and escarpment, soil depths might range
from 1 to 2 feet (0.3 to 0.6 meters) near
the top to 7 feet (2.1 meters) on the
slopes. The erosion potential on the slopes
is great and can be severe if vegetation is
removed.

Deposits at the foot of the Cumberland
Plateau escarpment consist of a mixture of
coarse, weathered rock and soil derived
primarily from upland Pennsylvanian
caprocks and Mississippian limestones.
These deposits are a mixture of materials
ranging from boulder-size sandstone
blocks to colluvium and alluvium.
Extensive areas of Quatemary alluvium
and colluvium from the caprock cover
flatter areas near the escarpment base.

Geomorphology

All of middle Tennessee was at one time
capped by a thick sequence of
Pennsylvanian sandstones,
conglomerates, and shales. Today, only in
the Cumberland Plateau area does the
caprock continue to protect the underlying
Mississippian limestones from relatively
rapid dissolution. The present topography
has been formed by continuous lowering
of the surface by erosion, a process that
involves slope retreat on beds of different
resistance.
Pennsylvanian sandstones were removed
by erosion from the Central Part of the
Nashville Dome (structural high along the
Cincinnati Arch) during the Mesozoic Era
and the underlying Mississippian
limestones were exposed. Slope retreat by
limestone dissolution then began forming
an escarpment and initiated its subsequent
retreat in all directions away from the
dome (Crawford 1982). Erosion continued
both downward and outward and a plainlike
surface developed upon the more cherty and erosion resistant
lower Mississippian rocks during the late
Cretaceous period (Miller 1974).

The resistant Mississippian Fort Payne
formation was breached by erosion during
the Tertiary and Quaternary Periods,
exposing the underlying Ordovician
limestones. This resulted in the Highland
Rim escarpment that is presently retreating
as the Central Basin expands. Dissolution
of the underlying limestones is primarily
responsible for the steep slope angles
along the Highland Rim and Cumberland
Plateau escarpments. Apparently, stream
erosion is occurring at about the same rate
along the Cumberland Plateau (Crawford
1982). Abundant caves and other karst
features associated with both escarpments
appear to have formed under very similar
conditions.

Along the escarpments of the Cumberland
Plateau are rather narrow but important
areas of karst. Caves and karst features
are abundant in this region, with most of
the larger caves occurring in the Monteagle
limestone near the base of the
escarpment. The base of the escarpment
usually corresponds to an area of cherty
St. Louis limestone and Warsaw formation. Maps of reported cave locations
in Middle Tennessee show highest
concentrations of caves along two
somewhat parallel lines that trend
northeast-southwest. The easternmost line
corresponds with the western escarpment
of the Cumberland Plateau while the other
corresponds with the escarpment of the
Highland Rim. In both locations, one finds
a similar relationship between erosion
resistant caprock and underlying weak
limestones.

The strata along the retreating Cumberland
escarpment are rarely horizontal. There is
also a strong correlation between caprock
removal by slope retreat and conduit cave
systems. Conduit caves along the
escarpment result primarily from
subterranean invasion of surface streams
flowing off of the plateau. This
invasion usually occurs near the contact
between the overlying Pennington
formation and underlying Bangor
Limestone. Water usually resurfaces on
top of the resistant Hartselle formation
halfway down the escarpment and reenters
the underlying Monteagle limestone.
Where the local dip is toward the
escarpment, caprock removal may
often be accelerated by subterranean
stream invasion occurring several miles
behind the retreating escarpment.

Hydrogeology

Geology. The Obed River watershed is
immediately underlain by gently dipping
Pennsylvanian sandstones, siltstones, shales,
some conglomerates, and coals.
These rocks have a thickness of about 1,500 feet
(457.2 meters). The Pennington Formation of
Mississippian age is a transition from the basal
Pennsylvanian sandstone and shale to
underlying Mississippian carbonate rocks that are
along the Sequatchie Valley escarpment, Grassy
Cove, and smaller cove areas south-southeast of
the watershed boundary.

The same mountain-building forces that resulted
in the Southern Appalachian Mountains and
deformed the rocks of the Valley and Ridge
formed the structures of the Cumberland
Plateau. Rocks along the eastern escarpment of
the plateau and many miles westward along
some zones were extensively faulted and folded. The structural trend is SWNE
like the Southern Appalachians. The
Sequatchie Valley, one of the largest and most
spectacular anticlinal valleys in the world, owes
(in part) its origin to these forces. At the
northeastern end of the anticline, massive
sandstone forms the Crab Orchard Mountains.
The anticline diminishes to the northeast and
disappears at the Emory River Fault zone. This
fault zone is part of a long belt of structural
deformation northwest of the Crab Orchard
Mountains. The belt is largely a series of thrust
faults that are connected by cross faulting and
anticlines (Swingle 1961).

Physiography

Cumberland, Morgan, and Fentress counties
which encompass the Obed WSR National
Park Service Unit lie in the Cumberland
Plateau physiographic province of
Tennessee. The terrain on the
plateau is distinguished by flat to rolling
upland areas (less than 10 percent slope),
deeply incised river gorges, and a long line
of cliffs that separate it from the lower
elevations of the Ridge and Valley Province.
In the northeastern portion of the upper
Emory River (which makes up the northeast
portion of the Obed WSR watershed), the
terrain is more mountainous. The area is
drained by a dendritic (fan-shaped) system
of streams that flow through the narrow
valleys.

Elevations in the watershed range from over
3000 feet (915 meters) above mean sea
level (MSL) in the mountainous upper Emory
River watershed to approximately 850 feet
(259 meters) MSL at Nemo Bridge, the
downstream end of the Obed WSR. Most of
the Obed WSR is influenced by the rolling
uplands on the plateau that exhibits a gentle
regional slope, varying from about 2000 feet
(610
meters) MSL near Crossville to 1300 feet
(396 meters) MSL at Wartburg. Elevations
along the lands bordering the streams within
the Obed WSR vary from 900 to 1500 feet
(274 to 457 meters) MSL. Some gorge
sections are quite narrow, only 800 feet (242
meters) across, and have near vertical sides,
up to 400 feet (121 meters) high.
The four principal streams of the watershed,
the Obed River, Clear Creek, Daddys Creek,
and the upper Emory River, drain
approximately 615 square miles (1,593
square kilometers) in Cumberland, Morgan,
and Fentress Counties. These high gradient
streams are similar to most other streams on
the Cumberland Plateau. Stream gradients,
with drops averaging 19 feet (5.7 meters) to
34 feet (10.4 meters) per mile, are steepest in
downstream sections. They have a distinct
meander pattern, developed on a higher
surface when the streams had reached a
temporary base level (perhaps on the
resistant Rockcastle Conglomerate). Table 4
lists the major streams and their drainage
areas at selected locations.

Only a short reach of the Emory River is
located within the Obed WSR boundaries.
That reach extends from the Emory River's
confluence with the Obed River, mile 28.4, to
Nemo Bridge, mile 27.7. Above mile 28.4
the Emory River drains an area of 91
square miles (3235.7 square kilometers).
Its headwaters are located in northeastern
Morgan County that exhibits some of the
most rugged terrain found in this region.

The Obed River is the largest tributary of
the Emory River and has a total drainage
area of 520 square miles (1,295 square
kilometers). Its headwaters are located a
few miles northwest of Crossville and the
stream flows easterly through a narrow
valley toward its junction with the Emory
River. The two principal tributaries, Clear
Creek and Daddys Creek, join the Obed a
few miles above its mouth. Little damage is
suffered from floods on the Obed River
because of the nature of the terrain and
the fact that there is little development or
farming near the stream. Damage to
highways and bridges constitute the chief
item of damage.

In the northwest portion of the watershed
lies the 173 square mile (448.1 square
kilometers) area drained by Clear Creek.
The stream flows north easterly from its
source near Campbell Junction to a point
near the Fentress-Cumberland-Morgan
county line, then southeasterly to its
junction with the Obed River about four
miles above the junction of the Obed and
Emory Rivers.

Daddys Creek, the largest tributary of
Obed River, drains an area of 175 square
miles (453.3 square kilometers). Its
headwaters are located south of the
Cumberland Homesteads, near Crossville.
From there the creek flows northeasterly to
its junction with the Obed River about nine
miles above the mouth.

The average stream slope of the Emory
River in the reach within the Obed WSR is
approximately 13 feet per mile. On Clear
Creek, the average slope in the 15-mile
reach investigated, Mile 0.00 to Mile 14.68,
is approximately 22 feet per mile with the
slope varying from 6 to 52 feet per mile.
The slope of the stream on Daddys Creek
in the 9-mile reach investigated, Mile 0.00
to Mile 9.10, averages approximately 39
feet per mile and varies from 17 to 70 feet
per mile.

Abandoned and Active Mines
Abandoned coal mines in the Obed/Emory
River watershed impact water resources within
the Obed WSR boundaries. Data regarding
the location of these mines is fragmented
between state and federal agencies. USOSM
data indicate a total of 40 mines are located in
the two watersheds, and state agencies have
data regarding mines permitted before
SMCRA legislation was enacted (prior to
1984). Impacts on the water quality of the
Obed WSR from active and abandoned mines
include increased sedimentation and turbidity,
and acid mine drainage. Although coal mining
has slowed in the watershed, an acceleration
of any mining activity could significantly impact
water quality in the Obed WSR.

Oil and Gas Exploration

Although oil and gas exploration in the
watershed has declined, some impacts to
water resOurces may still continue. At present
no monitoring program for oil and gas
operations is in place after the initial
installation inspection occurs. Active and
abandoned oil and gas operations should be
included in baseline land use assessment and
mapping projects, to assess impacts to the
Obed WSR.

The spectacular geology in our national parks provides the answers to many
questions about the Earth. The answers can be appreciated through plate tectonics,
an exciting way to understand the ongoing natural processes that sculpt our
landscape. Parks and Plates is a visual and scientific voyage of discovery!

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